The present invention relates to increasing the safety of a dental hygiene implement such as a light-emitting manual or an electrically operated motorized toothbrush which emits radiation, in the violet and/or blue region of the visible spectrum, between 400 nm and 500 nm, in order to:                oxidize and destroy potentially harmful bacteria and/or other contaminants or compounds contained within the mouth without harming or destroying human cells;        exert a phototoxic effect on pathogenic periodontal and oral bacteria such as; P. Gingivalis and F. Nucleatum, and S. Mutans;         activate a photo catalyst that may be deposited on the teeth and the gums of the person utilizing the toothbrush during normal brushing; and/or        accelerate the whitening effects of a tooth bleaching agent added to toothpaste or toothgel such as carbamide peroxide or hydrogen peroxide.        
The electronic interlock control mechanism in this toothbrush will reduce the possibility of accidental direct eye exposure to high flux visible light radiation emitted from this toothbrush when it is removed from the mouth.
Light-emitting toothbrushes have been developed over the past several years for teeth whitening applications in addition to the known oral hygiene benefits of regular brushing. When combined with a teeth whitening agent such as carbamide peroxide or hydrogen peroxide, studies have shown that light in the 400-500 nm range accelerates the whitening effect of these agents. Wolfgang Buchallaa, Thomas Attina: External bleaching therapy with activation by heat, light or laser—A systematic review; Karen Luk, D.D.S.; Laura Tam, D.D.S., M. Sc.; Manfred Hubert, Ph.D.: Effect of light energy on peroxide tooth bleaching. 
In addition, violet light in the 400 nm-420 nm range has been shown to have a phototoxic effect on pathogenic oral bacteria such as P. Gingivalis, S. Mutans and others. Michelle Maclean, Scott J. MacGregor, John G. Anderson, and Gerry Woolsey: Inactivation of Bacterial Pathogens following Exposure to Light from a 405-Nanometer Light-Emitting Diode Array. Doron Steinberg, Daniel Moreinos, John Featherstone, Moshe Shemesh, and Osnat Feuerstein: Genetic and Physiological Effects of Noncoherent Visible Light Combined with Hydrogen Peroxide on Streptococcus mutants in Biofilm. The inventors have previously shown the use of a Light-emitting Diode (LED) within a toothbrush provides anti-microbial properties of benefit to the oral hygiene of the end-user.
Current light-emitting toothbrushes have a manual on/off switch which activates the light-emitting device. This manual activation mechanism may lead to a safety risk because the user may activate the light and expose his or her eyes to high levels of light that may be harmful to the retina or optic nerve. The potentially harmful properties of visible light and maximum exposure levels are documented in ANSI standards. Francois C. Delori, Robert H. Webb, David H. Sliney: Maximum permissible exposures for ocular safety (ANSI 2000), with emphasis on ophthalmic devices. David H. Sliney, M. S.: Biohazards of Ultraviolet, Visible and Infrared Radiation. For example, the maximum permissible radiant power (thermal and photo-acoustic) entering a dilated pupil is 1.5×10-4 Watts. This limit would be exceeded if a user were to stare at a 420 nm LED of 250 mW radiant flux at a distance of 10 cm for a period of 0.5 seconds. To prevent accidental eye exposure a special electronic interlock control mechanism has been implemented to keep the optical source turned off if the toothbrush is not inserted in the users mouth and will turn the optical source off immediately if the toothbrush is removed from the mouth prior to completing the brushing cycle.
A toothbrush is typically used in close proximity to the eyes of the user, and if ocular exposure lasts several seconds, eye damage may happen. Furthermore, the ocular safety risk of manually activated light precludes the use of more powerful light-emitting devices such as high-powered LEDs, laser diodes, or vertical cavity surface emitting lasers, which would increase the teeth-whitening and antimicrobial benefits in proportion to the energy delivered. For example, studies show that effective whitening treatments require a minimum energy density of 30-50 J cm−2 to produce noticeable shade whitening. However, such energy levels would not be readily achievable with a typical two minute brushing interval using a low-powered LED that would also be safe when directly placed in front of the eyes, even when used over a period of several weeks. Similar limitations exist for the anti-microbial properties of violet light as well.
It is therefore desirable to control the “on” state of the light-emitting device to a time period when it is in use in the oral cavity but to shut “off” this high power light source immediately, when it is removed from the mouth to prevent direct eye exposure. This feature would also extend battery life of a battery operated brush since power is only used to illuminate the light source when in direct contact with the oral cavity.